This invention concerns a nonprecious, nonnickel, casting alloy for porcelain-bonded dental restorations.
A metal or alloy intended for dental restorations such as crowns and bridges must be strong, tough, biocompatible and resistant to tarnish, oxidation and corrosion in addition to being capable of forming precise castings. When the alloy is to be bonded to porcelain, it must additionally adhere well to the porcelain and having a coefficient of thermal expansion comparable to that of the porcelain.
The noble metals were used in preparing early dental restorations, since they are very effective for this purpose. Because of the high cost involved with such use, however, replacement of noble by nonprecious metals has constantly been sought. This search has focused primarily on nickel and cobalt based alloys, with numerous compositions being proposed.
Among the elements added to these nonprecious alloy compositions are gallium and indium, such additions being disclosed, for example, in U.S. Pat. Nos. 3,134,670, 3,907,555, 3,948,653, 4,038,074, 4,053,308, 4,229,215 and 4,255,190, and in Japanese Disclosed Application No. 31520/1978. These alloys, however, are in general rather complex, often containing ten or more elements. Also, the biocompatibility of nickel in dental applications has recently been questioned.
It is therefore a primary objective of the present invention to provide a nonprecious, nonnickel, dental casting alloy for porcelain bonding which is comparatively simple in nature and easy to prepare.